This invention relates to a method for the manufacture of an aluminum sheet of a prescribed thickness by the steps of compacting aluminum powder and treating the resultant green sheet of packed aluminum powder and further to a method for the manufacture of high-density sintered aluminum laminate by the steps of piling a plurality of green sheets of packed aluminum powder and treating the resultant pile of sheets.
SAP (Sintered Aluminum Powder) has been suggested as a method for the manufacture of sintered aluminum metal from aluminum powder. This method comprises converting fine aluminum particles produced from aluminum stock into aluminum powder containing alumina either by adjusting the oxide coat formed on the surface layer of said fine aluminum particles or by incorporating alumina from an external source, compression molding the alumina-containing aluminum powder, sintering the resulting mold by application of heat and then extrusion molding the sintered mold. However, it is extremely difficult to effect the manufacture of sintered aluminum metal continuously by this method.
Further, the aluminum powder generally has a stable oxide coat formed on the surface of its individual particles. For this reason, it is extremely difficult for a packed piece of aluminum powder to be sintered by application of heat at a temperature below the melting point of the packed aluminum powder.
There is also known a powder rolling process available for the production of sheets from powdered metal. This manufacturing process has been studied from various angles. To be commercially feasible, this process is required to be such that it can be carried out under continuous operation. Fundamentally, any process involved in the manufacture of a sheet from powdered metal generally comprises the steps of producing a green sheet of powdered metal, sintering the green sheet in a heating furnace and finally rolling the sintered sheet. In the case of aluminum powder, for the operation to be accomplished continuously, it is essential that the sintering of the sheet within the heating furnace be effected while the sheet is in motion at a fixed rate. Since the sheet is required to be retained within the furnace until sintering has been thoroughly effected thereon, the advantage of this process increases in proportion as the time required for the sintering is shortened. In order for the oxide coat formed on the fine aluminum particles to be melted, heating is required to be given at a temperature above at least 800.degree. C. To preclude the phenomenon of oxidation during the heating, the sintering must be carried out in an atmosphere without oxygen, namely, in the atmosphere of an inert gas such as argon, nitrogen or helium or of a reducing gas such as hydrogen. For successful continuous production of aluminum sheets on a commercial scale, this process has many technically difficult problems yet to be solved.
An object of this invention is to provide a method for continuously manufacturing, on a commercial scale, aluminum sheets excelling in mechanical strength and having a prescribed thickness from aluminum powder.
Another object of this invention is to provide a method for the manufacture of a high-density sintered aluminum laminate excelling in mechanical strength from aluminum powder.